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| Book | PreJuSER-31308 |
; ;
2003
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/248
Report No.: Juel-4091
Abstract: The revisited neoclassical transport theory for a collisional edge layer with steep radial gradients in the toroidal damping time scale is extended, to include the faster poloidal damping time scale. The evolution of the toroidal and poloidal rotation speeds is determined within the frame of neoclassical theory by two equations accounting for ambipolarity and momentum conservation. The timescales $\tau_{T}$ and $\tau_{P}$ for the evolution of toroidal, U$_{T}$, and poloidal, U$_{P}$, velocities are quite different and allow for an expansion with respect to $\tau_{P}$/$\tau_{T}$. The truncation of the expansion at the linear term, i.e., U$_{T}$=U$_{T0}$+U$_{T1}$, and U$_{P}$= U$_{P0}$+ U$_{Pl}$, yields four equations for U$_{T0,1}$ and U$_{P0,1}$: A diffusion equation for U$_{T0}$, an ordinary differential equation for U$_{P0,1}$ depending on the U$_{T0}$-profile, an evolution equation for U$_{T1}$, depending on the U$_{P0}$-profile are obtained by separating the secular parts from the fast varying parts. Resorting to TEXTOR-data and assuming in a first step a stationary profile for U$_{T0}$ the time evolution of U$_{P0}$ is computed, in particular it is shown that the U$_{P0}$ is, in general, close to its neoclassical value, but has the characteristic deviations at the boundary as demanded by the revisited neoclassical theory. In order to determine the stability behavior of poloidal and toroidal rotations in a tokamak plasma, the dependence of the poloidal velocity on time and initial velocity is analysed. It is observed, that the poloidal and toroidal spin-up tendencies are strongly coupled by nonlocal interactions, although these evolve essentially on différent time scales. Rotation speeds are also influenced by charge exchange interactions, neutral beam injection, or a radial polarization current.
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